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HD3SS213: Recommended Termination for (Undocumented) Unused Pins

Pedro Esteves
Prodigy 20 points
Part Number: HD3SS213

Hi !

We are using the HD3SS213 to multiplex CSI-2/D-PHY lanes, a different purpose than the standard use-case. As such, in our application the highlighted signals in red below are not used:

My question concerns termination for those signals, as the datasheet only states that the high-speed lanes are internally pulled down by 20k. I am not sure if the highlighted signals qualify, so I would like to double-check whether floating is okay or external termination is required - and if so, what kind and for which signals?

Finally, a more general question: do you foresee any potential problem by using the HD3SS213 with the purpose of  CSI-2/D-PHY multiplexing?
Many thanks in advance for your help,
Pedro

  • 0
    TI__Guru 64326 points
    Pedro,

    There should be no issues with leaving these pins floating. We have not used this device for this type of application but after reviewing the CSI/DPHY spec I could not find anything that jumped out as a glaring problem.
  • 0 in reply to Malik Barton57
    Prodigy 20 points

    Dear Malik,

    Very much appreciated for your feedback!

    If you don't mind, I have one additional question not stated on the datasheet, which is beyond the general layout recommendations: regarding the differential pairs, does the device have internal length matching, or is the maximum difference among the lanes somehow quantified? Otherwise, would you be able to provide me with a table of the relative (or absolute) lane lengths per differential pair (and, if not matched, within the same pair too)?

    Best Regards,
    Pedro

  • 0 in reply to Pedro Esteves
    TI__Guru 64326 points

    Pedro,

    This device does some internal length matching but there is a spec in the data sheet named "Inter-pair output skew" and "Intra-pair output skew" to account for any differences in data channels. Inter-pair output skew accounts for differences between channels (ex. DA1 to DA2). Intra-pair output skew is the difference between the P and N of a single channel (ex. DA1(p) to DA1(n) ). These specs and additional information is located in the HD3SS213 datasheet in section 6.6.(www.ti.com/.../hd3ss213.pdf)